To access hydrocarbon formations, a downhole assembly is lowered into a cased borehole in a well. A perforating gun or other tool connected to the downhole assembly is positioned adjacent to a hydrocarbon formation. The gun is detonated perforating the formation and fluid from the formation enters the borehole. The sudden surge of pressure in the well upon detonation of the perforating gun forces the equipment upward in the borehole. This surge of pressure may be caused by the denotation of the perforating gun or by the release of pressure from the formation. This sudden force may cause damage to the equipment. Surge anchors stop this sudden movement of the equipment by deploying slips which grip the casing wall and lock the equipment in position.
Anchoring devices are known to include a number of slip members with opposed camming surfaces which cooperate with complementary opposed frustoconical wedging surfaces. Such a device is disclosed in U.S. Pat. No. 4,345,649 issued Aug. 24, 1982 to Hughes Tool Company. This patent teaches a well packer having a seal assembly and an anchoring device. The anchoring device includes wedge members and slip members having complementary surfaces to cooperate with the surfaces of the wedge members. When the wedge members are moved into contact with the slip members through reaction to fluid pressure and piston movement, the slip members are pushed outward into contact with the well casing or liner. However, this anchoring device depends upon the shearing of set screws attaching the wedge members to the slip cage of the well packer. Once the screws have been sheared, the device cannot be reset in anchored relation to the well casing. Instead, the assembly must be removed from the borehole and the screws or the assembly replaced.
There therefore is a need for a device which can be repeatedly set to anchor a downhole assembly to a well casing.
There is also a need for an anchoring system which will automatically set when a surge occurs in a well.
There is also a need for an assembly which is simple in design and economical to manufacture and use.